Use this URL to cite or link to this record in EThOS: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.725797
Title: Evolution of the Tonga-Kermadec forearc in response to seamount subduction
Author: Funnell, Matthew James
ISNI:       0000 0004 6425 2119
Awarding Body: Durham University
Current Institution: Durham University
Date of Award: 2017
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Abstract:
Subducting plate characteristics are recorded as temporal variations in overriding plate deformation. Downgoing bathymetric anomalies superimpose enhanced tectonic erosion on pre-existing forearc crustal and sedimentary structural variations. Existing models of inherited forearc crustal structure along the Tonga-Kermadec subduction system are simplistic and neglect along-strike variability, which has resulted in a limited understanding of margin evolution and Louisville Ridge seamount chain (LRSC) subduction. In this study, robustly tested, velocity-depth and density-depth models are synthesised with existing data from the Tonga-Kermadec margin to reveal along-strike variations in the subducting and overriding plate structure. In regions north and south of the point of LRSC subduction, the incoming Pacific plate displays > 2 km-throw bend faults and reduced seismic velocity throughout the crust and upper mantle by ~1.0 km s⁻¹ and ~0.5 km s⁻¹, respectively. Around the LRSC-trench intersection, the trench axial depth decreases by 4 km and normal fault throw is reduced to < 1 km, suggesting the seamounts reduce subducting plate deformation. The forearc structure is dominated by the extinct (~51 Ma) Tonga arc, defined by a high velocity (7.0-7.4 km s⁻¹) and density (3.30 ± 0.10 g cm⁻³) lower crustal anomaly. Increases in Tonga-Kermadec forearc crustal thickness from 12 to > 18 km over 300 km along-strike are coincident with variations in bathymetry and free-air gravity anomaly that reveal a broader trend of northward-increasing crustal thickness between 18° and 32°, predating LRSC subduction at the margin. Beyond this region, the overriding crust formed as the south Fiji Basin opened ~35 Ma. Within this framework of existing crustal structure, LRSC subduction promotes erosion of the overriding crust, forming a steep unstable lower-trench slope. Following seamount subduction, trench-slope stability is re-established by the collapse of the extinct Tonga arc, suggesting that seamount subduction commenced at 22° along the margin.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.725797  DOI: Not available
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